1. Technical Field of the Invention
The present invention relates to stators for electric rotating machines that are used in, for example, motor vehicles as electric motors and electric generators.
2. Description of the Related Art
Conventionally, there are known stators for electric rotating machines which include a hollow cylindrical stator core and a stator coil.
The stator core has a plurality of slots that are formed in the radially inner surface of the stator core and spaced in the circumferential direction of the stator core. The stator coil is comprised of a plurality of electric wires mounted on the stator core. Each of the electric wires includes a plurality of in-slot portions, each of which is received in a corresponding one of the slots of the stator core, and a plurality of turn portions each of which connects an adjacent pair of the in-slot portions and is located outside the slots of the stator core.
Moreover, there is disclosed, for example in Japanese Patent Application Publication No. 2001-145286, a method of manufacturing a stator. According to the method, to improve the space factors of the electric wires in the slots of the stator core, each of the electric wires forming U-phase, V-phase, and W-phase windings of the stator coil is configured to have a rectangular cross section and have such an overall shape that when developed on a plane, the electric wire meanders in the form of cranks. Further, the stator coil is formed by: (1) stacking the electric wires to form a planar electric wire assembly; and (2) rolling the planar electric wire assembly by a predetermined number of turns into a hollow cylindrical shape.
For the thus-formed stator coil, it is necessary for corresponding in-slot portions of the electric wires which are to be received in the same slot of the stator core to be aligned in a radial direction of the stator coil. Further, to improve the space factor of the corresponding in-slot portions of the electric wires in the slot of the stator core, it is necessary to densely arrange the corresponding in-slot portions. As a result, insulating coats provided at the surfaces of the corresponding in-slot portions may be damaged due to friction which is caused between the corresponding in-slot portions during the step of rolling the planar electric wire assembly into the hollow cylindrical shape.
Moreover, with the above method, each of the electric wires is required to have a long length. Accordingly, a large scale shaping machine is needed for shaping the electric wires. Further, since each of the electric wires is long, it is difficult to handle the electric wires during the manufacture of the stator. As a result, it may be difficult to secure a high productivity and a low cost of the stator.